Dendroclimatic reconstruction of temperature in the eastern Qilian Mountains, northwestern China

Understanding the extent to which climate has varied in the past is a prerequisite to assessing current trends. In this study, we present a 225 yr tree-ring width record of Qinghai spruce Picea crassifolia from a mesic site in the eastern Qilian Mountains of northwest China. This tree-ring record showed significant positive correlations (p u003c 0.05) with temperature for most months from the preceding May to the current September, but none with precipitation or the Palmer Drought Severity Index. Based on the correlation relationships, we developed a regression model to reconstruct the average July temperatures over the period AD 1785-2009, which accounted for 45% of the observed temperature variation during the calibration period (1957-2009). This is the first tree-ring based temperature reconstruction in the eastern Qilian Mountains. The reconstruction indicated a warming trend that began around 1900 and continued through the late 20th century. Eight of the 10 warmest years were recorded during the period 1990-2009. The longest cool period occurred in 1894-1916. Comparisons of our reconstruction with other independent tree-ring based temperature reconstructions from the northeastern Tibetan Plateau suggest coherent variance patterns in these warm season temperature reconstructions regardless of the positive or negative correlation relationships between tree-ring records and temperatures. The results of comparisons also indicated that the warm season temperature variances lag behind the winter temperature variability by about 20 yr in this region.